Hepatic binding sites for angiotensen II in the rat

1. 125I-labelled (Asn1,Val5)-angiotensin II (125I-labelled AII) incubated with purified rat liver membranes was degraded with time, as estimated by three techniques: binding to an excess of specific antibody, polyacrylamide-gel electrophoresis and rebinding to fresh membranes. Degradation was inhibited in the presence of an excess of beta 1-24-corticotrophin but still very marked. 2. 125 I-labelled AII became bound to purified rat liver membranes. Association and dissociation rates were slow. Binding was competitively inhibited by (Asn1,Val5)-AII, (Asp1,Ile5)-AII and (Des,Asp1, Ile5)-AII. Apparent KD was approximately 0.1 nmol/l. 3. Bound hormone was also partly degraded independently of time. 4. Angiotensinases inhibitors had different effects on 125I-labelled AII binding. A clear increase was observed in the presence of beta 1-24-corticotrophin and phenylmethylsulphonylfluoride whereas binding was decreased in the presence of EDTA or 8-hydroxyquinoline. 5. These results demonstrate the presence of high-affinity binding sites for AII and of angiotensinases in hepatic membranes.